Humans are beset with a variety of vascular abnormalities, among them arteriovenous malformations, arteriovenous fistulas, and aneurysms. Two very serious cerebral vascular ailments are arteriovenous malformations and aneurysms. Arterial-venous malformations, commonly referred to as AVMs, are a fibrous mass of intertwined, directly connected arterial and venous vessels. That is, the artery will branch into numerous smaller arterial vessels that in turn feed directly into the numerous veins. An AVM located in the brain therefore deprives certain areas of the brain of the blood needed for proper functioning. As the AVM steals blood from normal brain parenchyma, the theft of blood can create a variety of disease states or brain malfunctions, including but not limited to epilepsy and transient ischemic attacks. One of the considerable risks associated with AVM growth is that the AVM will burst, leading to intracerebral bleeding.
An aneurysm is an abnormal bulge in the wall of a blood vessel that develops as a result of a weakness in the vessel wall. Aneurysms can take two forms: sacular and fusiform wherein a portion of or the entire circumferential extent of the vessel wall is implicated, respectively. Aneurysms can rupture, leading to cerebral bleeding and can cause a patient to have a stroke or to die. An arteriovenous fistula is a direct fluid connection between an otherwise fluidically isolated artery and vein.
A number of techniques and procedures have been developed to deal with AVMs and aneurysms. Both have been treated through surgery. During a surgical procedure to treat an AVM, the skull is opened and the feeding arteries and outgoing veins are ligated. The AVM is then excised. This procedure will normally require some cutting and removal of brain tissue. In addition, there have been several minimally invasive procedures developed to treat these vascular ailments. For example, AVMs have been treated by inserting a catheter into a patient and guiding it to the location of the AVM. A glue is then released that forms a plug and blocks the artery feeding the AVM. The blood is diverted back into the normal blood flow path as a result.
Aneurysms have also been treated by various techniques. Surgical treatment of an aneurysm will typically involve exposing the aneurysm and then applying a clip to the neck of the aneurysm to close off the aneurysm from the vessel, thereby re-establishing normal circulating blood flow in the treated vessel. One minimally invasive procedure involves delivering a catheter to the point of the arterial or venous aneurysm and then releasing a coiled wire into the aneurysm itself. Once released, the wire uncoils to fill the aneurysm. Blood tends to clot around the coiled wire, thus sealing off the aneurysm. Another minimally invasive procedure, known as Hunterian ligation, involves placing a detachable balloon via a catheter at the location of the aneurysm, inflating the balloon, and then releasing it, thereby completely occluding the artery. Yet another minimally invasive procedure involves placing a detachable balloon inside the aneurysm itself, inflating it and detaching it.
While effective, the prior known techniques of treating vascular ailments, particularly cerebral vascular ailments, carries with them certain risks that are preferably avoided. For example, open cranial surgery carries with it risks of infection, hemorrhaging, anesthetic risks, organ function failure, stroke, paralysis and death. Minimally invasive procedures like treatment of AVMs with glue can be difficult because the blood flow through the AVM will inhibit the solidification of the glue at the proper location. In addition, the glue plug may loosen or dissolve over a time, leading to the reoccurrence of the AVM, that is, the recanalization or reopening of the previously occluded vessel. As for treating an aneurysm with a coiled wire, the wire is left in the brain in the midst of a forming clot. The clot or portions thereof can break away into the blood stream and can cause a stroke. In addition, the coiled wire has been known to spontaneously dislodge and migrate through the vascular system. Likewise, the use of a balloon to treat an aneurysm has its share of risks, among them premature balloon detachment, rupture after inflation and detachment, and migration. Migration can lead to an unexpected and undesired distal vessel occlusion, which can in turn lead to brain ischemia and ischemic stroke.
In summary, treatment of vascular abnormalities presently involves either surgical intervention or minimally invasive procedures that in some situations operate to occlude the vasculature (AVMs) and in others to occlude the abnormality itself (aneurysms). Both procedures offer the possibility of severe risks, however.
It has recently been proposed to use radio frequency electrical current for intraluminal procedures. U.S. Pat. No. 5,098,431 to Rydell is an example of such proposed use. Such proposals involve insertion of a current carrying guide wire into a lumen and then energizing the exposed electrode. As the current passes from the electrode, the surrounding luminal fluid is heated as well as the lumen wall. As the temperature of the fluid and lumen increases, the cells in the lumen wall begin to dry, leading to possible rupture of the cell walls. In this manner, the lumen could be severed. This use thus corresponds to electrocautery. The effects on the lumen with this procedure are difficult for the surgeon to control.
Reduction, restriction, or occlusion of the various lumens being treated with radio frequency (rf) electrical energy coupled to the lumen walls with a virtual electrode, would reduce or eliminate some or all of the foregoing risk factors. In this procedure, a conductive solution is introduced into the site where it is desired to affect the tissue. An electrical current is then supplied to the conductive fluid via a metal electrode electrically coupled to an rf current generator to create a virtual electrode. The virtual electrode spreads the supplied current to the walls of the vessel. Typically, the greatest resistance or impedance to the flow of the rf current will be at the interface between the virtual electrode and the vessel walls, leading to initial heating at the site of the interface, that is, the vessel walls. Stated otherwise, the vessel walls have a greater resistance to the passage of current and like all non-superconducting materials begins to heat as the rf current is supplied.
As the resistance of the vessel walls leads to heating, the temperature of the vessel walls begins to rise and the connective tissues found in the vessel walls begin to depolymerize and shrink, causing the vessel to collapse inwardly in a radial direction and to shorten in a longitudinal direction. In this manner, then, a vessel, a segment or wall portion of a vessel, or other body lumen or segment or portion thereof such as a blood vessel, fallopian tube or bronchiole, could be shrunk as desired to the point of being completely occluded.
It would be desirable to have an apparatus and method for treating vascular ailments, in particular cerebral vascular ailments, and for performing other intraluminal procedures, that is not subject to the foregoing disadvantages, that can be performed using minimally invasive surgical techniques, that will provide a permanent solution to the ailment or treatment to the condition being affected, and that is safer than prior known techniques for treating such ailments.